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C&C 27 Association – Props
The following is information submitted to the Forum on prop choices. Negative opinions have been provided along with positive ones to give a sense of the range of possibilities. If you have a match that isn't covered (or that is, and you'd like to reinforce comments here), please let us . All props are 2-blade, right-handed unless otherwise noted.
Most shafts are 7/8" but there are reportedly some 1" out there. The taper is probably SAE (aka, 'Standard'), but you should ask a prop shop to check. These boats are old enough that a previous owner may have slipped something different in there.
Many people don't like the Martec and Michigan Wheel non-geared folding props because they have little reverse thrust, but non-geared props are relatively inexpensive when new (from Martec – MW has dropped their line), cheap when used and have a very small frontal area compared to geared props, hence slightly less drag. They do get worn with use, but can be refurbished at prices better than new. Martec operates its own refurbishing service; in addition many prop shops can do the required work.
Prop walk - All props "walk" to one side, particularly in reverse when starting from stationary (the stern of a 27 with a standard engine and prop setup swings to port when put in reverse). The way to avoid this is to get some way on the boat and some flow over the rudder so it is effective in counteracting the swing. (3-blade props have the reputation of being less prone to walk, not because they are inherently less prone to it, but because even at low revs, their far greater blade area and consequent thrust gets the boat moving more quickly and the rudder working more effectively, before the stern starts to walk.)
Instead of putting the engine in gear and easing on the throttle, shift into reverse and give the engine a shot of power; in other words, rather than accelerating from idle to 1,000 rpm, run up to 1,500 or so, but just until the boat begins to move. At that point, drop back to a point midway between 1,500 and idle. That little shot of power will give you enough motion to allow your rudder to bite, and if you give your rudder a touch of starboard helm to counteract residual walk, you'll exit your slip under control and straight as a die.
Do something similar when stopping - rather than easing into reverse, shift and give the engine a good shot of power. That burst of reverse thrust will stop the boat reliably and quickly enough that there is no time for prop-walk.
"After I saw someone handling a boat this way, I took out a C&C 34 (with a Martec folder, a worst-case combo) and practised around a plastic buoy (so I could run into it with impunity). In short order I could put that boat anywhere I wanted. It wasn't difficult - in fact it was fun - and since then, I've had no qualms about putting Towser or any other boat anywhere." - David Weatherston
Vibration in props – First, the vibration may not be in the prop; misalignment of the engine, insufficiently tight coupling bolts, a badly worn or very slightly bent shaft, or a worn cutless bearing may be the root cause. Overtime, a Mk V, had a persistent problem that was solved by going to a Martec. Subsequent investigation showed that the limit stops on the original Gori had worn, so the prop was opening into an uneven state, unbalancing it. Sometimes it would smoothe out after running for some time, sometimes not. Owner Dave Moores related, "My mechanic showed me where the limit-stops on the Gori get flattened over time and allow the blades to go over-centre. Unless the wear is exactly symmetrical each blade takes a slightly different angle and that causes the vibration."